Plasticizers represent, alongside rubber and fillers, another important class of additives in the rubber mixtures used for tires (pneumatic tires, bicycle tires, solid rubber tires) and in industrial rubber items (hoses, drive belts, other belts, printing blankets, membranes, gaskets, air springs, bellows, automobile-interior cladding, synthetic leather). Large amounts of plasticizers are sometimes added to rubber mixtures, in order to reduce the cost of the mixture, to improve the flow properties of the mixture (energy saving during processing, avoidance of energy peaks), to improve filler dispersion, to improve packing and adhesion behavior, and to influence the physical properties of the mixture and of the vulcanizates produced therefrom.
Almost all of the plasticizers used in the rubber industry are generally based on petroleum. For environmental reasons, especially with a view to the current levels of pollutant emissions and current shortages of raw material, petroleum is no longer an acceptable starting material for future production of rubber plasticizers. Alternatives used as plasticizers in rubber mixtures are by way of example vegetable oils, as described for example in DE 101 08 981 A1 and U.S. Pat. No. 7,335,692. The vegetable oils described in those publications can be used as sole plasticizer, but are mostly used in combination with another plasticizer obtained from petroleum. However, the vegetable oils are also subject to limitations on amounts available to the rubber industry.
U.S. Pat. No. 8,236,875 describes, as another alternative, the use of what are known as BTL oils (Biomass-To-Liquid oils). Solid biomasses are starting material for the production of the plasticizers here, which can in turn proceed by various routes. Examples that may be mentioned are flash pyrolysis, with very short residence times in the reactor, direct liquefaction with hydrogenation, where use of (pressurized) hydrogen during the pyrolysis produces stable hydrocarbon products, the process known as the Carbo-V process, which is based on the Fischer-Tropsch process, and direct catalytic liquefaction, in which the pyrolysis proceeds in a sump, with addition of catalyst. Direct liquefaction processes are described in very general terms by way of example in DE 102 15 679 A1 and DE 10 2005 040 490 A1.
A direct liquefaction process for biomass is disclosed in Willner, Marktfruchtreport [Report on commercial agriculture] 2005, Mitteilungen der Landwirtschaftskammer, Landwirtschaftskammer Schleswig-Holstein, Kiel.
However, the problem here is that there are restrictions on the amount of biomass available. If BTL production is used on a larger scale in the future, not only for fuels but also for plasticizer oils, this will therefore lead to land- and utilization-based competition brought about by the increased utilization of agricultural and forestry land. The cost of harvesting, transport, shredding, et cetera also has to be considered.